Optical disc recording media are generally for recording data. The recorded data on the optical disc may be read and retrieved by commercial optical disk drives. Conventional recordable optical discs are formed by a substrate and have their surfaces coated sequentially with a dielectric layer, a recording layer, and a reflective layer, and finally are covered by a protective overcoat.
The recording materials used by the recording media mentioned above usually include Ag—In—Sb—Te, In—Sb—Te, or Ge—In—Sb—Te. The media thus made generally are called CD-RW and are available on the market, Records on flee CD-RW generally are formed by irradiating a high power semiconductor laser of the wavelength about 780 nm. A portion of the recording layer materials being irradiated are transformed from the crystallized region to the amorphous region and result in a reliable burning effect. As the crystallized region and the amorphous region have different reflectance, signals burned on the CD-RW may be read sequentially by a lower power laser beam. The substrate of the CD-RW set forth above has wobble grooves, The frequency of the wobble grooves contains Absolute Time In Pre-groove (ATMP). The noise-signal ratio of the wobble grooves is above 36 dB before burning, and above 26 dB after burning.
In contrast, conventional CD and CD-ROM discs do not have any recording layer. All of the data are engraved in advance on stampers. Then an injection principle is employed to replicate the pits on the substrate. The substrate is plated with a reflective layer to complete the CD or CDROM disc. The information formed by the pits are read to control the rotation speed of the disc and obtain time signals. The signals formed by the pits no longer contain wobble information.
Recently there are patents suggesting to make hybrid discs to combine the read-only area formed by pits and the rewritable area formed by grooves. Such discs are generally called Hybrid Discs in the Orange Book. For the hybrid discs, one of the critical techniques is to make the electric signals regenerated from the read-only area and the rewritable area to meet the standards of the Orange Book. However on the hybrid discs designed by directly adopting the conventional technical specifications of CD or CD-RW, the electric signals regenerated from the read-only area and the rewritable area are difficult to simultaneously meet the standards of the Orange Book.
In the presently known hybrid discs, the composition of the read-only area and the rewritable area differs greatly from the conventional CD or CD-RW. For instances, U.S. Pat. Nos. 5,316,814, 5,696,758, 6,115,353 and 6,212,158 disclose various types of techniques for making the hybrid disc. They directly adopt the pre-pit and pre-groove specifications of the conventional CD and CD-RW. The differences are:                1. In order to simplify manufacturing processes, the layers being plated on die read-only area and the rewritable area on the hybrid disc must be the same. However, the read-only area of the conventional disc requires only one plated reflective layer. In contrast, the read-only area and the rewritable area on the hybrid disc must be plated with a dielectric layer, a recording layer, a reflective layer, etc. to form a laminated structure.        2. In the known hybrid discs, tile pre-pit of the read-only area and the pre-groove of the rewritable area have different depths. The depth of the pits of the conventional CD-ROM usually ranges from 80 nm to 160 nm. Only signals of high frequency modulation can reach this standard. However the depth of the grooves of the conventional CD-RW is smaller, and usually ranges from 30 nm to 80 nm. The width of half-depth groove generally ranges from 400 nm to 800 nm. Based on the groove reflective index of the CD-RW of these specifications, only high frequency modulated signals can reach the Orange Book standards. In the presently known hybrid discs, as the depths of the pre-pit in the read-only area and the pre-groove in the rewritable area are directly adopted the conventional CD and CD-RW specifications, engraving the grooves on the stamper is very difficult.        3. The known hybrid discs require the frequency of the wobble grooves to carry ATIP to link the read-only area and the rewritable area, hence the pits in the read-only area also contain wobble signals. Therefore both the read-only area and the rewritable area must conform to the Orange Book standards (WCNRa),        
Making the stamper for a conventional hybrid disc, as shown in FIG. 1(A) generally includes forming a photoresist film 11 at a thickness ranged from 30 nm to 160 nm on a glass substrate 10; then as shown in FIG. 1(B), employing a laser beam to cut the photoresist film 11 to form pits 12 with the bottom ends reaching the surface of the glass substrate 10. The maximum depth of the pits 12 is the thickness of the photoresist layer 11. Thus to cut and form the pits 12 with the required depth does not need to control the energy of the laser beam.
However, cutting the grooves 13 is different. In order to meet the Orange Book standards, in the presently known products that adopt the groove depth of the conventional CD-ROM, to cut the groove with the depth between 30 nM and 80 nm requires strict control of laser beam energy. Taking the median value of 55 nm as the basis, the upper and the lower allowance is merely 25 nm. With so small of tolerance, production yield is very low. Moreover, there is still a distance between the bottom end of the groove 13 and the surface of the glass substrate 10, and the bottom end of the groove is pointed because of We characteristics of the laser beam. The pointed bottom end of the groove results in not desirable signal regeneration and burning.
After having fished the manufacturing processes set forth above, the back surface of the finished product is plated with silver or nickel to form the master disc. The master disc then is polished on the back surface and cut to form the stamper for producing the hybrid optical discs.
For the engraving machines now available, to engrave the pits and the grooves of two different depths and widths on the same photoresist film is very difficult. As a result, production cost for such type of stamper is very high and control of the yield is very difficult. Therefore it is critical to develop an improved hybrid optical disc.